Wetland Conditions Differentially Influence Nitrogen Processing within Waterfowl Impoundments

Abstract

Manipulating hydrologic conditions at the land-water interface is critical for managing wetland functions. Hydrologic manipulation to increase retention time of water is used to promote wetland conditions, enhance nitrogen (N) processing for reduced N export, and attract migratory bird populations. Human managed wetlands such as waterfowl impoundments are intended to attract waterfowl for tourism. The limited literature has shown that waterfowl impoundments export N during seasonally prescribed drawdowns; however, it is unknown how impoundment-specific characteristics and different types of impoundments influence N cycling transformations. We compared seasonal N cycling between and within moist-soil managed (MSM) and agricultural (Ag) waterfowl impoundment soils. Potential nitrification, denitrification, and N mineralization rates and soil physicochemical properties were analyzed. Potential nitrification and denitrification rates were higher in the Ag compared to MSM impoundment even when the MSM site is actively managed to promote wetland conditions year-round. Despite the higher soil organic carbon and soil moisture content at MSM compared to Ag site, the high extractable soil ammonium, low nitrate, and low nitrification rates at MSM are evidence of substrate limitation for denitrification but not nitrification. These results indicate that decoupling of nitrification and denitrification could explain the reduced N removal capacity in these managed wetlands.